Battery mAh to Wh Converter
Convert a battery's capacity from mAh (or Ah) to watt-hours by entering the charge rating and the nominal voltage. Useful for comparing batteries, estimating runtime, and checking airline lithium-battery limits.
Convert Battery Capacity from mAh to Watt-Hours
mAh to Wh Formula
Where:
- \(E\) — energy in watt-hours (Wh)
- \(C\) — charge capacity in amp-hours (Ah); if the rating is in mAh, divide by 1000 first
- \(V\) — nominal voltage of the battery (V)
The formula multiplies the charge a battery can deliver by its voltage, converting a charge rating (mAh) into the actual amount of stored energy (Wh).
mAh to Wh – Calculation Example
Example: a typical power-bank cell rated at 5000 mAh with a nominal voltage of 3.7 V.
\[ C = \frac{5000\ \text{mAh}}{1000} = 5\ \text{Ah} \]
\[ E = 5\ \text{Ah} \times 3.7\ \text{V} = 18.5\ \text{Wh} \]
Result: the battery stores 18.5 Wh of energy.
How to Use the Calculator
- Enter the charge capacity printed on the battery or its data sheet in the Battery Capacity (C) field.
- Choose the matching unit — mAh or Ah — from the dropdown next to the input field.
- Enter the battery's nominal voltage in the Nominal Voltage (V) field (e.g. 1.2 V for NiMH, 3.7 V for a single Li-ion cell, 7.4 V for a 2S Li-ion pack).
- Read the Energy result in watt-hours (Wh) and the Capacity in Amp-Hours result, along with a step-by-step breakdown in Calculation Details.
What mAh and Wh Actually Measure
Milliamp-hours (mAh) describe charge: how much electric current a battery can supply over time. A 5000 mAh cell can, in theory, deliver 5 A for one hour or 0.5 A for ten hours. But charge alone does not tell you how much energy the battery holds, because energy depends on the voltage at which that charge is delivered.
Watt-hours (Wh) describe energy: power multiplied by time. One watt-hour is the energy consumed by a 1 W device running for one hour. Since power equals current times voltage, energy equals charge (Ah) times voltage (V) — which is exactly what this calculator computes. If you need to convert between related units, our power unit converter handles watts, kilowatts, and other power units, and the time unit converter helps when working out runtime figures.
This distinction matters when comparing batteries. Two power banks both rated at 10,000 mAh are not equal if one is a 3.7 V single-cell design (37 Wh) and the other a 7.4 V two-cell design (74 Wh). The second stores twice the energy. Marketing numbers usually quote mAh because they look bigger, but Wh is the honest, voltage-independent measure of what a battery can do.
Wh is also the unit regulators use. Airline rules for lithium batteries are stated in watt-hours: typically up to 100 Wh is allowed in carry-on baggage without approval, and 100–160 Wh requires airline approval. To check whether your power bank or spare battery is within the limit, convert its mAh rating to Wh with this calculator.
Typical Nominal Voltages by Chemistry
| Battery type | Nominal voltage |
|---|---|
| Alkaline cell (AA/AAA) | 1.5 V |
| NiMH rechargeable | 1.2 V |
| Li-ion / LiPo single cell | 3.7 V (3.6–3.85 V depending on chemistry) |
| LiFePO4 single cell | 3.2 V |
| 2S Li-ion pack | 7.4 V |
| 3S Li-ion pack | 11.1 V |
| Lead-acid (6-cell) | 12 V |
If the voltage is not printed on the battery, check the data sheet or the device's charging specification. For multi-cell packs, the nominal voltage is the single-cell voltage multiplied by the number of cells in series.
Assumptions and Limitations
- Nominal voltage is used, not the full discharge curve. A Li-ion cell actually swings from about 4.2 V down to 3.0 V during discharge. The nominal voltage (3.7 V) is an average, so the calculated Wh is a good approximation, not an exact measurement.
- Rated capacity assumes specific conditions. Manufacturers quote mAh at a standard discharge current and temperature. Real usable capacity is lower at high loads, low temperatures, or when the device cuts off before the battery is fully drained.
- Conversion losses are not included. If a power bank boosts 3.7 V up to 5 V to charge a phone, roughly 10–20% of the energy is lost in the conversion circuitry. A 37 Wh power bank will deliver around 30 Wh to your device.
- Use the battery's own voltage, not the output voltage. If a power bank is rated "10,000 mAh at 3.7 V", the mAh figure refers to the internal cell — enter 3.7 V. Some brands advertise mAh at 5 V, which inflates the number; when in doubt, compute Wh and compare those.
Frequently Asked Questions
How do I convert watt-hours back to mAh?
Divide the energy by the voltage, then multiply by 1000. The reverse formula is \( C_{\text{mAh}} = \frac{E_{\text{Wh}}}{V} \times 1000 \). For example, a 74 Wh battery with a 7.4 V nominal voltage holds \( 74 / 7.4 \times 1000 = 10{,}000 \) mAh. Always use the battery's nominal (cell) voltage, not a charger's output voltage, or the mAh figure will be wrong.
How many mAh equals the 100 Wh airline limit?
It depends on the battery's voltage. For a typical 3.7 V power bank, \( 100 / 3.7 \times 1000 \approx 27{,}000 \) mAh, so anything up to about 26,800 mAh usually qualifies. For an 11.1 V laptop pack, the same 100 Wh limit corresponds to only about 9,000 mAh. Airline staff check the Wh rating printed on the device, so verify your battery against the limit for its actual voltage rather than mAh alone.
Why does my 10,000 mAh power bank not charge my phone 2–3 times?
The power bank stores 10,000 mAh at 3.7 V internally (37 Wh), but your phone's battery also holds roughly 10–15 Wh. The boost converter that raises 3.7 V to the 5 V charging port loses 10–20% of the energy, and the phone's own charging circuit loses more. In practice expect roughly 60–70% of the rated energy to reach your device, so about two full charges of a modern phone is realistic.
What voltage should I enter for a power bank that says 5V output?
Enter the internal cell voltage, typically 3.7 V for Li-ion, not the 5 V USB output. The mAh rating on most power banks refers to the cell. Some brands advertise capacity at 5 V to inflate the number — dividing their mAh by the same 5 V gives the correct Wh either way, but mixing a cell-based mAh with 5 V overstates the energy by about 35%. When in doubt, compare batteries in Wh only.
How can I estimate how long a battery will run my device?
Divide the energy in Wh by the device's average power draw in watts: \( \text{runtime (h)} = E_{\text{Wh}} / P_{\text{W}} \). A 37 Wh power bank running a 5 W device gives roughly 7.4 hours. For a constant-current load you can also divide Ah by the current in amps. Real runtime is somewhat shorter because of converter losses, voltage sag, and cut-off before the battery is fully drained.
Is a battery with more mAh always better?
No — mAh alone ignores voltage, so it only lets you compare batteries of the same chemistry and cell configuration. A 3,000 mAh 3.7 V cell (11.1 Wh) stores far less energy than a 3,000 mAh 11.1 V laptop pack (33.3 Wh). Always convert to Wh before comparing different battery types. Also note that higher capacity usually means larger size and weight, so the best choice depends on your energy needs and portability.
How do I convert mAh to kWh or mWh?
First convert to Wh using \( E = \frac{C_{\text{mAh}}}{1000} \times V \). Then scale: 1 kWh = 1000 Wh, and 1 Wh = 1000 mWh. For instance, a 5000 mAh, 3.7 V battery holds 18.5 Wh, which is 18,500 mWh or 0.0185 kWh. Household electricity meters measure kWh, so this conversion is useful when comparing battery storage against grid energy consumption.